The present invention relates to planarizing pads and methods for making and using planarizing pads in mechanical and chemical-mechanical planarization of semiconductor wafers, field emission displays, and other microelectronic device substrate assemblies.
Mechanical and chemical-mechanical polishing processes (collectively xe2x80x9cCMPxe2x80x9d) remove material from the surface of microelectronic substrates in the production of microelectronic devices and other products. FIG. 1 schematically illustrates a rotary CMP machine 10 with a platen 20, a wafer carrier 30, and a planarizing pad 40. The CMP machine 10 may also have an under-pad 25 between an upper surface 22 of the platen 20 and a lower surface of the planarizing pad 40. A drive assembly 26 rotates the platen 20 (indicated by arrow F), or it reciprocates the platen 20 back and forth (indicated by arrow G). Since the planarizing pad 40 is attached to the under-pad 25, the planarizing pad 40 moves with the platen 20 during planarization.
The wafer carrier 30 has a lower surface 32 to which a wafer 12 may be attached, or the wafer 12 may be attached to a resilient pad 34 under the lower surface 32. The wafer carrier 30 may be a weighted, free-floating wafer carrier, or an actuator assembly 36 may be attached to the wafer carrier to impart axial and/or rotational motion to the wafer 12 (indicated by arrows I and J, respectively).
The planarizing pad 40 and the planarizing solution 44 defame a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate 12. The planarizing pad 40 can be a fixed-abrasive planarizing pad having abrasive particles fixedly bonded to a suspension material. In fixed-abrasive applications, the planarizing solution is generally a xe2x80x9cclean solutionxe2x80x9d without abrasive particles. In other applications, the planarizing pad 40 can be a non-abrasive pad composed of a polymeric material (e.g., polyurethane, polycarbonate or polyester), felt, resin or other suitable materials. The planarizing solutions 44 used with the non-abrasive planarizing pads are typically CMP slurries with abrasive particles and chemicals.
To planarize the wafer 12 with the CMP machine 10, the wafer carrier 30 presses the wafer 12 face-downward against the planarizing pad 40. More specifically, the wafer carrier 30 generally presses the wafer 12 against the planarizing liquid 44 on a planarizing surface 42 of the planarizing pad 40, and the platen 20 and/or the wafer carrier 30 moves to rub the wafer 12 against the planarizing surface 42. As the wafer 12 rubs against the planarizing surface 42, the planarizing medium removes material from the face of the wafer 12.
CMP processes should consistently and accurately produce a uniformly planar surface on the substrate to enable precise fabrication of circuits and photo-patterns. During the fabrication of transistors, contacts, interconnects and other features, many substrates develop large xe2x80x9cstep heightsxe2x80x9d that create highly topographic surfaces. Such topographical surfaces can impair the accuracy of subsequent photolithographic procedures and other processes that are necessary for forming sub-micron features. For example, it is difficult to accurately focus photo patterns to within tolerances approaching 0.1 micron on topographic surfaces because sub-micron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical surface into a highly uniform, planar surface at various stages of manufacturing microelectronic devices.
One problem with many CMP processes is that the surface of the wafer may not be uniformly planar because the rate at which material is removed from the wafer (the xe2x80x9cpolishing ratexe2x80x9d) may vary from one area of the wafer to another. The characteristics of the planarizing pad generally influence the variance of the polishing rate globally across the substrate surface and also at a smaller scale across the individual dies (xe2x80x9cchipsxe2x80x9d) on the substrate. For example, hard or incompressible planarizing pads quickly remove high points on the substrate to produce a good planarity across the individual dies, but hard pads generally produce large variances in the polishing rate in a band about 10 mm inward from the perimeter edge (xe2x80x9cedge effectsxe2x80x9d). Hard pads may thus produce poor global planarity on a substrate. Soft or compressible planarizing pads, on the other hand, generally produce good global planarity because they mitigate edge effects, but soft pads may follow the topography between dies and periphery areas such that they produce xe2x80x9cdomingxe2x80x9d over the individual dies. Soft pads accordingly produce poor planarity at a die level on a substrate. Therefore, neither hard nor soft pads produce good planarity at a global level without producing doming over the dies.
To resolve the problems associated with hard and soft planarizing pads, several conventional pads have a combination of soft and hard materials including a soft base layer and an inflexible, hard planarizing layer on the base layer. The planarizing layer contacts the surface of the substrate during a planarizing cycle and the base layer distributes differences in pressure between the pad and the substrate. Although such two-layer pads provide an improvement over single-layer pads, the hard planarizing layer still produces edge effects on the substrates in many applications. This drawback is expected to become even more prominent for CMP of twelve-inch wafers instead of eight-inch wafers.
The present invention relates to planarizing pads and methods for making or using planarizing pads to polish or planarize semiconductor wafers, field emission displays, or other microelectronic substrates and substrate assemblies. In one embodiment, the planarizing pad comprises a compressible body and a plurality of discrete contact elements. The compressible body can comprise a base having a backside facing a support surface of a table and a front side facing away from the support surface. The contact elements can comprise raised sections of a single layer or separate plates. The contact elements have a bottom surface attached to the front side of the base and a top surface facing away from the base. The compressible body has a first hardness and the contact elements have a second hardness greater than the first hardness, and/or the compressible body has a first compressibility and the contact elements have a second compressibility less than the first compressibility. The compressible body can be a compressible foam (e.g., foamed polyurethane), and the contact elements can be a hard, rigid material (e.g., polycarbonate, resin, polyester, or high density polyurethane). In operation, the contact elements can move independently from one another in a direction transverse to the substrate.